One side arc welding has been practiced for many years. Examples of such technology is disclosed in Crockett et al. U.S. Pat. No. 5,945,014, Shutt U.S. Pat. No. 4,246,463 and Fratiello U.S. Pat. No. 5,155,330, all of which are fully incorporated herein by reference as background to the present invention.
When welding butt joints, it is often advantageous to perform the arc welding process from a single side with the plates generally horizontal so the electrode used to deposit metal can move along the flat heavy plates at the joint between the edges of the plate to perform the joining operation. This type of welding is used, for example, to weld large oil rigs which require large segments of steel plates to be joined together for constructing the pontoon area of the oil rigs. Pulse arc welding is also used in shipbuilding for ship and submarine hulls and deck plate to weld thick heavy plate with out of position welding, such as fillet welds, T-joints, square butt joints, lap joints and groove welds. The thick heavy plates used on ship hulls eliminates concerns about blow through and there is less concern in those applications for the quality of the back bead as further finishing welds or processes are performed due to the criticality of such welds.
Plates and pipe are also commonly welded using a technique known in the art as root pass welding. Root pass welding may be a single side type of welding operation for joining two heavy steel plates having their edges butted together, or for welding pipe joints. The butt joint used for root pass welding may be formed as a single-V preparation joint in which the facing edges of the workpieces have a tapered edge to define a channel. Below this channel is a backing material such as a copper block, for example, having a recessed cavity. This recessed cavity is filled with a granular flux to help form the back side of the weld bead as the root pass or first layer of molten metal is applied along the bottom portion of the channel between the edges of the heavy steel plates. Other mediums, such as fiber tape and ceramic tile, may also be used to form the backside of the weld bead.
The single-V preparation joint is typically characterized by each facing edge being formed as a knife edge, or alternatively a tapered edge with a land. The facing edges that are to be joined may abut each other, referred to as zero gap, or may have a prescribed gap therebetween. Root pass welding is commonly done with short arc welding so as to prevent blow through and overheating at the weld joint. Short arc welding is also commonly used on root pass joints because there is less drooping and suck back. Short arc welding is also typically used on thinner work pieces because of less penetration with a smaller puddle and lower heat input. Short arc welding typically is also a slow process.
The Crockett et al. patent noted above provides a very useful technique for performing root pass welding on steel plate. The process uses pulse arc welding with a backing material, and may use variable frequency pulses to control heat.